This invention relates generally to turbine engines and more specifically to clearance control systems used with gas turbine engines.
Known gas turbine engines include an engine casing that extends circumferentially around a compressor, and a turbine that includes a rotor assembly and a stator assembly. Known rotor assemblies include at least one row of rotating blades that extend radially outward from a blade root to a blade tip. A radial tip clearance is defined between the rotating blade tips and a stationary shroud attached to the engine casing.
During engine operation, the thermal environment variations in the engine may cause thermal expansion or contraction of the rotor and stator assemblies. Such thermal expansion or contraction may not occur uniformly in magnitude or rate. As a result, inadvertent rubbing, such as between the rotor blade tips and the casing may occur, or radial clearances may be created that are wider than the design clearances which may adversely affect engine performance. Continued rubbing between the rotor blade tips and engine casing may lead to premature failure of the rotor blade.
To facilitate minimizing inadvertent rubbing between the rotor blade tips and the surrounding shroud or undesirable large radial clearances, at least some known engines include an active clearance control system. The clearance control system channels cooling air to the engine casing to facilitate controlling thermal growth of the engine casing and to facilitate minimizing inadvertent blade tip rubbing. Such cooling air may be channeled from a fan assembly, a booster, or from compressor bleed air sources. The effectiveness of the clearance control system is at least partially dependent upon controlling pressure losses that may occur while the cooling air is channeled towards the engine casing.